Coupled Events in the Early Biochemical Actions of FSH on the Sertoli Cells of the Testis

Abstract

Over the past several years this laboratory has been concerned with attempting to define in chemically precise terms the temporal sequence of events which occur upon the initial interaction of FSH with its testicular target cells. Previous studies have revealed that a single injection of this gonadotropin to immature male rats results in a rapid stimulation of RNA and protein synthesis (1–3). It is well established that FSH is a polypeptide hormone composed of two dissimilar subunits. Since studies with other peptide hormones such as insulin, glucagon, ACTH and LH have demonstrated that these hormones apparently do not enter the cell but instead bind specific receptors present on the surface of the target cell, we wished to investigate this possibility with respect to FSH and the testis. Our initial studies were made possible by the development of a procedure by van Lenten and Ashwell (4) for the radio-labeling of glycoproteins with tritium. Vaitukaitis and colleagues applied this procedure first to hCG (5) and then to FSH (6). Tritiation of the FSH involved oxidation of the carbohydrate side chain with periodate followed by reduction with tritiated borohydride. This procedure results in more than 85% of the tritium attached to the C7 position of sialic acid which comprises the terminal carbohydrate residue of the FSH side chain. FSH, radiolabeled in this fashion maintained a high biologic activity (1400 IU/mg) although the specific radioactivity was only about 0.25 mCi/mc.